I have emboldened and colored
all direct objects (direct objects are nouns that receive the action
of transitive verbs in the active voice).

In 1831 the manager of a Hudson's Bay Company post in northern
Ontario wrote to the head office in London. The local Ojibway Indians were
starving, he reported, because of a scarcity of "rabbits," and they were unable
to trap for furs because they spent all their time
fishing for food (Winterhalder 1980). These shortages of so-called rabbits,
which apparently occurred approximately every 10 years, are regularly mentioned
in Canadian historical documents from the 18th and 19th centuries. Those rabbits
were in fact snowshoe hares (Lepus americanus), and their 10-year cycle
is one of the most intriguing features of the ecology of the boreal forest.

Ten-year cycles were first analyzed quantitatively when wildlife
biologists began to plot the fur trading records [records is the object of
an infinitive phrase but it is not a direct object] of Hudson's Bay Company
during the early 1900s. The Hudson's Bay Company, established in 1671, kept
meticulous records of the numbers of furs
traded from different posts spread across Canada. The most famous time series
drawn together from those records was that of Canada lynx (Elton and Nicholson
1942; Figure 1). The lynx is a specialist predator of snowshoe hares, and
the rise and fall in lynx numbers mirrors, with a slight time lag, theriseand fall
of snowshoe hare populations across the boreal region.

The spectacular cycles of snowshoe hares and their predators
have captured the attention of biologists
as well as historians. These cycles are highlighted in virtually all ecology
texts and are often cited as one of the few examples of Lotka-Volterra predator--prey
equations, a simple model which shows never-ending oscillations
in the numbers of predators and their prey. Cycles seem to violate the implicit
assumption of many ecologists that there is a balance in nature, and anyone
living in the boreal forest would be hard pressed to recognize a balance among
the boom and bust in nature's economy. The challenge to biologists has been
to understand the mechanisms behind these cycles, which has not been easy.
One cycle lasts 10 years, and few PhD students or researchers wish to take
10 years to obtain n = 1. Fortunately, over the last 40 years ecologists working
in Alberta, the Yukon Territory, and Alaska have put together an array
of studies that have resolved most, but
not all, of the enigmas behind these cycles (Keith 1990, Boutin et al. 1995).

To understand any fluctuating population, one must first know
in detail the mechanisms of changes in
births, deaths, and movements that are the proximate causes of the changes
in numbers. Before we describe these details,
we should note that these 10-year hare cycles tend
to occur in synchrony across broad regions[here
the entire dependent clause functions as noun and direct object].
Indeed, hares across most of Canada and Alaska reached a peak in 1997-1999
during the most recent cycle. We explain the reasons
behind this synchrony below, but let us note here that movements of hares
cannot explain thesepopulationchangesvia immigration or emigration. Movements on a local level might be important,
but at the regional level all populations rise and fall in unison. Population
changes must be driven by changes in births and deaths.